Content area
Full Text
Key Words sensitization, learning, nucleus accumbens, dopamine, drug abuse
* Abstract The development of addiction involves a transition from casual to compulsive patterns of drug use. This transition to addiction is accompanied by many drug-induced changes in the brain and associated changes in psychological functions. In this article we present a critical analysis of the major theoretical explanations of how drug-induced alterations in psychological function might cause a transition to addiction. These include: (a) the traditional hedonic view that drug pleasure and subsequent unpleasant withdrawal symptoms are the chief causes of addiction; (b) the view that addiction is due to aberrant learning, especially the development of strong stimulusresponse habits; (c) our incentive-sensitization view, which suggests that sensitization of a neural system that attributes incentive salience causes compulsive motivation or "wanting" to take addictive drugs; and (d) the idea that dysfunction of frontal cortical systems, which normally regulate decision making and inhibitory control over behavior, leads to impaired judgment and impulsivity in addicts.
CONTENTS
INTRODUCTION
Many people experiment with potentially addictive drugs. About 60% of Americans sample an illicit drug at least once in their lifetime, and even after excluding marijuana, the lifetime prevalence for illicit drug use is about 32% (Johnston et al. 2001). If alcohol is included, the percentage of Americans exposed to a potentially addictive drug rises to over 90%, but few of these people become addicts. Even for a very addictive drug like cocaine, only 15-16% of people become addicted within 10 years of first use (Wagner & Anthony 2002). Substantial numbers of people do become addicts, of course, but the fact remains that drug use does not inevitably lead to addiction. Addiction is more than mere drug use. It is defined specifically as a compulsive pattern of drug-seeking and drug-taking behavior that takes place at the expense of most other activities. The key questions in addiction, therefore, are why do some susceptible individuals undergo a transition from casual drug use to compulsive patterns of drug use, and why do addicts find it so difficult to stop using drugs (Edwards 1981)?
To address these questions requires some consideration of how drugs affect the brain. Thus, much research on the transition to addiction has aimed at identifying and characterizing brain systems...